Plain-language summary:
The current dry and sunny weekend with
low humidity is an exception in the current pattern. Rain, heavy at times, will
return later tomorrow and will be the most widespread on Tuesday before the
storm leaves on Wednesday. A widespread 1-3” (25-75 mm) and locally up to 4-5”
(100-125 mm) of rain is likely, leading to more flooding in flood-prone areas,
especially from the Adirondacks and southern Quebec on east, which has already
seen excessive rain since July. Warmer and somewhat drier conditions are
expected later in the week, though scattered showers and thunderstorms cannot
be ruled out given uncertainty in exact timing and position of weather systems
and fronts. Hotter and more humid air could gradually dominate into the
following week, but with frequent chances of showers and thunderstorms still
likely, keeping the flood threat elevated.
Meteorological discussion:
With high pressure in control, this
weekend is mostly sunny with low humidity and temperatures just a tad below
average, except northern Maine which will still see a few showers due to the closer proximity to an upper-level low over the Gulf of St. Lawrence. That has been a rarity since late June! Today will be a few degrees
warmer than yesterday with the sunshine modifying a previously cool Canadian
air mass, and tonight will be noticeably warmer than last night with light
southerly flow ahead of the next storm gradually bringing in warmer and more
humid air.
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| Source: TropicalTidbits |
It seems like every time a drier spell
looks to arrive, it ends up being short-lived with an unexpected slow-moving and
moisture-rich storm bringing more heavy rain afterward. This theme continues
this week, with a storm on Monday and Tuesday originally expected to go farther
north, allowing for little more than scattered showers and thunderstorms in our
area, instead going right over our area, with a fetch of very moist air from
the western Atlantic. With the low-pressure system lifting the moist air, most
areas will receive 1-3” (25-75 mm) of rain, but locally up to 4-5” (100-125 mm)
is possible. Given the soggy ground from the insanely wet July, especially from
the Adirondacks and southern Quebec on east, and some storms earlier this week,
flooding will become a concern yet again. With the low-pressure center tracking
near or along the St. Lawrence river valley, rain will be steadier with much
below average temperatures to the north, with warmer and more humid air and scattered
to widespread showers and thunderstorms to the south. Given the wetness and
clouds though, nowhere in our area will have truly hot temperatures.
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| Source: TropicalTidbits |
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| Source: PivotalWeather |
Most of the rain will fall from southern
Quebec to western Vermont on westward during the day on Monday and will be rather light in the initially dry air mass, with a warm and
mostly sunny day expected to the east. The rain, including some heavier convective rains from the southwest, will overspread the entire area
by late Monday night, with Tuesday being wet almost everywhere, with Maine
and the Laurentians being especially rainy and chilly due to being north of the low-pressure center
with overrunning rain and upsloping easterly flow. By Wednesday, the storm
center will have moved to New Brunswick, with cool and cloudy conditions
with a few remaining showers prevailing from central Vermont eastward, especially northwest of the Appalachians with
upslope flow.
By Thursday, ridging will build in
briefly, with warmer and drier conditions expected. A cold front could approach
the area later Thursday or Friday, sparking more typical summertime scattered
showers and thunderstorms, mostly in the afternoon with daytime heating induced
instability. The models are struggling with handling the position and timing of
the different shortwave disturbances, especially those that have the potential
to cut off from the main jet stream, like the Monday/Tuesday system that was
originally expected to stay farther north and joint with the main jet stream. Generally
though, given the main trough axis just to the west, we can expect frequent disturbances
sparking scattered showers and thunderstorms, with seasonably warmer and more humid
conditions, akin to what we saw in mid-July, albeit slightly cooler.
 |
| Source: TropicalTidbits |
Ridging may gradually become more
dominant, especially in southern and eastern areas, with a ridge setting up
over the West Coast and another one south of Atlantic Canada, and the ridging
over northwestern Canada weakening. However, any troughs that move eastward
from the main trough axis in the Plains and Midwest U.S. will trigger more
showers and thunderstorms with locally heavy downpours, especially given the moist
southwesterly flow ahead of the disturbances. The ever present -NAO, though weakening, could also continue
to allow a slower than usual movement of weather systems and unusually far
south and strong low-pressure systems cut off from the main jet stream like we
have seen since June, especially with +PNA and ridging over the West Coast. If this outlook is accurate, the warm (but not very hot),
humid, and wet pattern from July could return by mid-August, with more flooding
potential given the recent wetness. It seems like though that recently, every prediction
of ridging and hotter weather in the long-range busts or is delayed.
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| Source: TropicalTidbits |
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| Source: Climate Prediction Center |
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